Conventionally, an image forming apparatus is known in which images of individual colors are formed on photoconductive drums by a laser optical system, then the images of the individual colors are superimposed on a transfer belt to form one color image, and the color image is transferred to a sheet. In the image forming apparatus, at the time of warm-up such as when power is turned on or at the time of recovery from sleep, relative misalignment between components of the laser optical system is generated by temperature rise within the apparatus and may cause a shift between the superimposed images of the individual colors. Therefore, alignment of the images of the individual colors is carried out at the time of warm-up.
The shift between the images of the individual colors may also be caused by relative misalignment between the components of the laser optical system due to the lapse of time. Therefore, alignment is also carried out when a prescribed number of sheets is reached in copying, and when a prescribed operation time is reached in copying and the ready state.
However, in the conventional image forming apparatus, the formation of color images must be waited for or interrupted in order to carry out alignment.